The continued purpose of this clinical research center project is to study the clinical problems arising from various insults to the ear. The effects of noise and drug damage upon hearing is being studied. Identification of the agents which interact to produce auditory damage is being pursued. Basic mechanisms involved in ototoxicity and noise-induced damage are being investigated at the level of single unit responses in the VIII nerve, as well as by surface preparation histology and electron microscope. Continued studies will involve assessment techniques of recording the inner ear electrophysiology, the endolymphatic potential, N1 potentials, cortical evoked potentials, and behavioral responses from conditioned animals. In addition anatomical confirmation of damage are rendered by surface preparation histology, serial sectioning, and in some cases electronmicroscopy. Progress has been made and work will continue in the identification of which forms of the aminoglycosides are and are not ototoxic and with constant antibacterial potency. The conditions under which ototoxic drugs potentiate the damaging effects of noise have been revealed and work will continue to further define relevant conditions. The ever-present condition of tinnitus associated with many otologic insults has been studied. Two relief procedures (both using masking) have been developed and work with them will continue. It is important to determine under what conditions they are effective.